Guys, I've had a random miss for months, really longer than that.

The car is heads/cam/longtubes...the 224/230 cam has a little lope to it but not much...but the car has what feels just like a miss at idle, its not rythmic though, its random. It has been setting Random Missfire code P0300 on occasion too. When the miss hits the dash lights will flicker slightly.

Also, on the dyno last month the car was cutting out really bad...both cruising at 70 before I went WOT and during each pull...it would just cut out and miss all the way up the range as if it was momentarily shutting off.

Now the coil, module, wires, and plugs are all new. The opti is new too, as I put it on when the heads/cam went on 3 mos ago. I chalked the whole thing up to a faulty new opti, and just got done doing the LTCC coilpack conversion. The miss is still there.

its hard to feel the cutting out on the road, but I'm pretty sure its still doing it...you can sort of feel a hesitation at steady cruise..like its momentarily cutting out.

I thought it could still be the optical side of the opti since it still drives the LTCC, but if that were so I'd expect the timing to be off and the car to be backfiring and studdering, it does not do this however, its a simply miss/cutting out.

So I am left with 2 things in my brain...bad ground or misadjusted valves. I have not re-adjusted the valves since the cam went in but I believe they are right. 1. the miss was there even with the old cam/heads. 2. It is not a constant steady miss, it is random. If a valve were open all the time, it would be a steady miss.

So what else? I'm basically needing input from anyone who has had an odd miss and found the fix. Sensors? TPS maybe? Alternator related issues?

The ground strap is secure, I've already checked it. No intake vacuum leaks, just re-installed the intake manifold last week with no change. No vacuum leaks, nothing to speak of.

I do have a wild fuel trim split at idle that is not steady...it changed...I believe this is related to the miss.

I just need ideas. Thanks.

 

i have been there for both the track runs and the dyno pulls... and its not like one cylinder is cutting out at a time... its like the whole engine was cutting out at WOT... 40 hp dips on the dyno curve... and the PT and idle problems are evident as in the lights seem to flicker when it happens on idle...

i am lost at this point...any help??

 

Are you getting any knock retard? I have a similar problem. Do you have a LT4 KM?

 

Its not timing retard related...I have the knock retard function disabled at WOT...LT4 km is installed but I don't see how that could possibly cause a miss much less ignition cutting out at WOT.

 

the light flickering thing has me thinking something w/ ground or some sort of short somewhere.

 

I agree...that's almost all that's left at this point, the alternator guts are new...perhaps it is somehthing to do with one of the 2 alternator wires.

 

its worth checking. but what else is there if that isn't it???

any one else have any ideas?

 

Yeah I forgot about what you said with the lights flickering. I'd say that it's the alternator ground most likely. I've heard of that wire causing ignition woes before.

 

Thanks. I wish somebody with experience with alt ground problems would chime in.

 

So this morning, just to test a theory, I started the car up then pulled the + batter cable. Theory was that if it was alternator related, that removing the battery from the system would unmask the problem, and the car would either die when the miss occurred or it would miss worse and then pick back up.

Neither happened, it was about the same. But then something did happen. I turned the car off, re-attached the battery, and started back up. The car ran like garbage, just like a carb car witht the choke on. I had to pedal it to keep it running as it did not want to idle. It finally died. So I disconnected and reconneced the + cable 1 more time, and after that it ran just like normal (meaning same original condition, not "fixed" normal).

Makes me think there is indeed something up in that + battery cable harness, which also includes I believe the starter + wire, the red alternator ground wire.

 

maybe the + battery cable is bad???

 

You know how I've had the ABS INOP light for a year now despite pulling the ABS codes and replacing the rear sensor?

I've been running searches like mad here and have seen several situations where low voltage and/or dying alternators caused the ABS light to come on.

 

could be that... guess its worth checking out... if it doesn't fit it just take the new one back to NAPA...

 

You could also check the ground bolt that screws into the passenger fender. I had an ABS Inop light one time and it turned out to be that the ground bolt was not tight. That could also be a bad ground for your mis...possibly.

 

Where on the fender is this ground located memphis?